This invention relates to permanent magnet generators and more particularly to a highly-efficient permanent magnet generator driven by a clockspring to produce output voltage of short duration.
The electrical theory behind permanent magnet generators is well understood: a permanent magnet having north and south poles is rotated between two or more pole pieces which provide a flux path magnetically linked to a wound wire coil such that rotation of the permanent magnet induces an alternating voltage in the coil. It is also well understood that the intensity or magnitude of the voltage is dependent upon the time rate of change of the flux passing through the pole pieces and this time rate of change is in turn a function of the speed at which the permanent magnet is rotated between the pole pieces.
The present invention is in essence a small, highly-efficient permanent magnet generator based in operating principle on the electrical theory described above and driven by a clockspring to produce an output voltage of short duration. In general, the clockspring generator of the present invention comprises a wound wire coil, a magnetically efficient and easy-to-assemble frame structure which provides pole pieces on the interior of the coil and a magnetically permeable structure which essentially cages or encloses the coil. The generator further comprises a rotor having a portion which passes through the center of the coil and frame structure so as to rotatably locate a permanent magnet between the pole pieces of the frame structure. In the preferred form, a flat wound clockspring is mechanically mounted between a shaft portion of the rotor and a portion of the frame structure to hold the assembly in a unitary state and to drive the rotor for a short time duration to produce an output voltage in the 15- to 30-volt range.
As hereinafter described, an illustrative and preferred embodiment of the invention comprises a bobbin-mounted coil, a rotor of non-magnetic material having disc and shaft portions, a two-pole permanent magnet mounted within a larger diameter portion of the rotor such that the poles are laterally arranged, inner and outer cup-shaped frame members of magnetically permeable material which are formed in such a fashion as to define opposed pole pieces, annular top and bottom plates and circumferentially spaced interleaved walls to cage the coil and bobbin combination and provide shallow recesses on the top and bottom of the assembled structure. The rotor is assembled to this combination of inner and outer frames such that the shaft projects through the center of the coil cage and locates the permanent magnet between the pole pieces which are defined by the inner and outer frame members respectively. Disc-like brass bushings are added to the assembly to eliminate friction and improve the overall mechanical and electrical operating efficiency of the structure. The caging structure of the cup-shaped frame members effectively shields the coil against the effects of stray magnetic fields. The coil spring holds the assembly together and may be wound to arm the generator by means of slots in the bottom of the rotor disc.